I set up my country drop down and my category drop down here are some screenshots and a video. I selected a larger mile radius when searching because I have location sensor on and am in US and that particular map has center map at Charleston SC. Various settings shown, you can have any fir category, cascading or single, or you can leave first entry blank to have first category appear in drop down.
you can see video at “https://youtu.be/JW9UKGcYdJI”